Main reason: the will to own an "enthusiast product". The measurable, technical benefits aren't even that important. It's more satisfiyng to have a special case than a random one, which may be good and fully functional, but is nothing special. After all, we build our PCs not only because we need something to work or play with, but also because we enjoy this process. It's a hobby.

I also got me a 1000W PSU, one of the best there is. It costs like two or three times more than a normal 500W quality PSU, which would be more than enough for my PC, but I still decided to get the Seasonic. I have absolutely no technical benefit by having such a PSU, maybe it's even a deficit as the efficiency at low load levels may be worse than what a good 500W PSU can achieve. I still bought it because I just did want to have it. That's it. For me it's satisfying and I'm happy, for others it's "throwing out money for no reason".

I can understand the viewpoint of others, but they cannot understand mine.

50 € cases don't come anywhere near to supporting the amount of hardware some of us have (or had), not to mention you do generally get better quality as you head up the price scale. I've been there with all the £25 cases in the past, many years ago. There's just no comparison. Cheaper cases are good for test rigs or cheap ones, but absolutely awful when it comes to optimising temperatures and noise (and making it look like you put value in your system). I can warrant a "cheap korean monitor" that actually looks and performs awesome in all regards (moreso than my Acer which cost £100 more), but i couldn't warrant putting £1400 worth of hardware into a £25 case.